rt2x00: Fix firmware loading regression on x86_64.

Commit 6175ddf0 changes the way
memcpy_toio() works for x86_64, causing firmware loading to fail for
some Ralink WLAN devices with the rt2800pci driver since linux 2.6.34.
This causes the log message: "phy0 -> rt2800pci_load_firmware: Error -
PBF system register not ready.".

Fix this by using __iowrite32_copy instead of memcpy_toio().

Signed-off-by: Wolfgang Kufner <wolfgang.kufner@gmail.com>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>